Causes

Bleeding per rectum can originate from the stomach, duodenum, small intestine, colon or anorectum (Table 20.1). The diagnosis of colorectal neoplasia should be entertained in most cases: 1 in 20 patients over the age of 45 years of age who present with new onset rectal bleeding have colon cancer. The colour of the blood may indicate the source of the bleeding but the rate of bleeding needs to be taken into account. Haematochezia is the passage of bright red blood per rectum and usually indicates bleeding from the distal colon, rectum or anal canal. Dark red blood mixed in with bowel motions usually originates from the small intestine or proximal colon. Melaena, the passage of black tarry stools with characteristic odour, occurs with bleeding proximal to the ligament of Treitz.

TABLE 20.1 Causes of rectal bleeding

Causes of massive rectal bleeding

Common causes of massive rectal bleeding include colonic diverticular disease and angiodysplasia. Diverticula in the colon are caused by increased intraluminal pressure together with segmentation of the colon resulting in herniation of mucosa through the muscle wall. Bleeding from diverticular disease is usually a large amount because it results from direct trauma to the adjacent penetrating vessels. It is uncommon for patients to present with diverticulitis and bleeding because the pathogenesis of the two is different. Diverticulitis results from micro-perforation of colonic diverticula. The inflammation is located on the outside of the colon with minimal intraluminal involvement. Ischaemic colitis is a more likely diagnosis if a patient presents with abdominal pain, fever, and rectal bleeding. Angiodysplasia are venous ectasia at the submucosal level and are more frequently found in the right side of the colon. They can be treated with electrocautery or argon plasma coagulation.